V 2 O 2 F 4 (H 2 O) 2 H 2 O: a new V 4+ layer structure related to VOF 3 Cameron Black and Philip Lightfoot* School of Chemistry, EaStCHEM, University of St Andrews, KY16 9ST Correspondence email: pl@st-andrews.ac.uk Abstract The title compound, V 2 O 2 F 4 (H 2 O) 2 H 2 O, (I), features a new infinite, V 4+ -containing, two-dimensional layer, comprised of fluorine bridged corner-sharing and edge-sharing VOF 4 (H 2 O) octahedral building units. Synthesis was carried out under solvothermal conditions. The V 4+ centre exhibits a typical off-centring, with a short V=O bond and elongated trans V F bond. Hydrogen bonded water molecules occur between the layers. The structure is related to previously reported vanadium oxyfluoride structures, in particular the same layer topology is seen in VOF 3. 1. Introduction Our recent work has focused on the preparation of V (IV) oxyfluorides due to their interest as frustrated magnets. We have found that the successful synthesis of two-dimensionally connected vanadium (IV) oxyfluoride structures, for example kagome lattices, requires the use of ionic liquids as solvents (Aidoudi et al., 2011a, 2011b & 2014, Clark et al. 2015). On the other hand, there have been several previous reports of solvothermally synthesized vanadium compounds incorporating selenium, which are generally two-dimensional and three-dimensional in nature, and can attribute this highdimensional structural property to the incorporation of selenium-based anionic linkers (Nguyen et al., 2011 & Glor et al., 2011). Reduced, dimensionally extended vanadium compounds can also be prepared by these routes, for example VO(SeO 2 OH) 2 (Kim et al., 2010) and (4,4 -Bipyridine)V 2 Se 2 O 8 (Dai et al., 2003). During solvothermal synthesis experiments, aimed at producing two-dimensional and three-dimensional vanadium (IV) selenites with triangular lattices, a new V 4+ layer structure, V 2 O 2 F 4 (H 2 O) 2 H 2 O, (I), was discovered (Fig. 1). This is apparently the first example of a fully reduced V 4+ layered compound synthesized by solvothermal (rather than ionothermal) techniques. The structure is comprised of VOF 4 (H 2 O) corner and edge-sharing octahedral building units. V 2 O 2 F 4 (H 2 O) 2 H 2 O, (I) (or VOF 2 (H 2 O).1/2 H 2 O), is structurally related to previously synthesized vanadium oxyfluoride compounds, VOF 3 (Supel et al., 2007). 2. Experimental Vanadium trifluoride, VF 3, (Alfa, 98%; 0.002 mol, 0.215 g) and ethylene glycol (Fisher 99%+; 0.0032 mol, 0.2 ml) were added to 0.5 ml of a 40% solution of HF (Alfa). Diethylamine * (Sigma, 99.5%; 0.001 mol, 0.5 ml) and selenious acid (Aldrich 99.999%; 0.001 mol, 0.129 g) were added to the resultant mixture before being sealed in a teflon lined steel autoclave. This was heated at 120 C for 4 days, then allowed to cool to ambient temperature. The final product was filtered, washed in water and allowed to dry overnight at 60 C. Crystals were blue blocks, indicating V 4+, of typical dimension 0.06 x 0.04 x 0.03 mm. These were separated from the bulk product, a brown powder, under an optical microscope. Crystals recovered were too scarce to be analysed using powder X-ray diffraction or to be sent for elemental analysis. * Guanidine carbonate salt (0.001 mol, 0.09 g) was used in a different experiment in place of diethylamine and produced similar results. Crystal data, data collection and structure refinement details are summarized in Table 1. Crystals of (I) are monoclinic, in the space group C2/c. Hydrogen atoms were located from Fourier maps and refined isotropically. 1
3. Results and discussion The VOF 4 (H 2 O) building unit of (I) exhibits a single vanadium site in a distorted octahedral environment (Fig. 2), and a single uncoordinated water molecule. The short V=O bond length along with the longer trans V F and cis V OH 2 bond lengths are comparable to those seen in the cis-building unit of [C 6 H 4 N 22 ][VOF 4 (H 2 O)] 2 H 2 O, (II). (Aldous et al., 2007). Selected bond lengths for (I) and (II) are shown for comparison (Table 2). The octahedral units are linked via fluoride ligands to produce a new two-dimensional corner and edge-sharing layer compound of V 4+ (Fig. 3a). Bond valence sum analysis (Brese et al., 1991) confirms the oxidation state of the vanadium centre as V 4+, oxidized in situ from V 3+ (Table 3). The layer in (I) resembles that of the VOF 3 structure (III) (Supel et al., 2007), with both forming a layer comprised of corner and edge-sharing octahedral units bridged via fluoride ligands (Fig. 3 b). Aside the different vanadium oxidation states, there are a number of significant differences between these two structures. The presence of uncoordinated water molecules in (I) results in longer inter-layer V V distances, due to the H-bonding from O3 to the layer (O3 H2, 1.861 (44) Å and H2 O2, 0.858 (43) Å), compared to those in (III) (Table 4). The elongated trans fluoride ligand, F1, in (I) is involved in the edge-sharing V F bonds, while in (III) the equivalent ligand is involved in the corner-sharing V F bond. This results in a significant difference in the intra-layer V V distances (Table 4). The layers of (I) can be seen to stack in a "staggered" manner (Fig. 4a.), while the layers in (III) stack in an "eclispsed" manner (Fig. 4 b.) when both are viewed along [010]. There are many previous examples of layered V 4+ containing compounds that have synthesized solvothermally (Nguyen et al. 1995; Massa et al., 2002), however, these compounds owe their two-dimensional structural properties to phosphate and sulfate linkers. More recently there have been examples of V 4+ containing layers, synthesized via ionothermal methods (Aidoudi et al., 2011a, 2011b & 2014). These compounds exhibit two-dimensional layers comprised fully of V 4+ corner-sharing octahedral units. This appears to make compound (I) the first example of a purely V 4+ layered compound produced via solvothermal techniques. From the presented synthesis route, compound (I) appears as a minor phase, together with a majority unidentified phase(s). Several further attempts to prepare (I) as the majority phase were unsuccessful. The synthetic method will need to be refined in order to produce (I) as the bulk phase, but this could lead to a simpler, more cost-effective route, compared to ionothermal techniques, to obtain layered V 4+ compounds for physical property investigation. Table 1 Experimental details Crystal data Chemical formula F 4 H 6 O 5 V 2 M r 263.93 Crystal system, space group Monoclinic, C2/c Temperature (K) 173 a, b, c (Å) 14.453 (8), 4.8879 (19), 9.663 (5) β ( ) 103.24 (2) V (Å 3 ) 664.5 (6) Z 4 Radiation type Mo Kα µ (mm 1 ) 2.87 Crystal size (mm) 0.06 0.04 0.03 Data collection Diffractometer Rigaku SCXmini diffractometer 2
Absorption correction Multi-scan REQAB (Rigaku, 1998) T min, T max 0.742, 1.000 No. of measured, independent and 3138, 750, 585 observed [I > 2σ(I)] reflections R int 0.115 (sin θ/λ) max (Å 1 ) 0.646 Refinement R[F 2 > 2σ(F 2 )], wr(f 2 ), S 0.035, 0.071, 1.01 No. of reflections 750 No. of parameters 63 H-atom treatment All H-atom parameters refined Δρ max, Δρ min (e Å 3 ) 0.56, 0.67 Computer programs: CrystalClear (Rigaku Corp., 2004), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), Diamond (Brandenburg, 2009), WinGX (Farrugia, 1999). Table 2 Selected bond lengths (Å) for comparison between (I) and cis & trans-(ii). Relevant bond lengths are also shown for (III). Compound Bond Bond length (I) V1 O2 1.592 (2) V1 F1 2.174 (2) V1 O1 2.027 (3) cis-(ii) V2 O3 1.641 (3) V2 F5 2.084 (3) V2 O4 2.035 (3) trans-(ii) V1 O1 1.606 (3) V1 F3 1.960 (2) V1 O2 2.305 (3) (III) V1 O1 1.551 (2) V1 F1 1.972 (2) V1 F3 2.294 (2) Table 3 Bond valence parameters. Atom Σ s (ij) V1 3.942 O2 1.676 a F2 0.514 b F1 0.482 b F2 0.477 b O1 0.517 a F1 0.276 b s (ij) values calculated for B = 0.37; (a) Brown & Altermatt (1985). (b) Brese & O Keeffe (1991). 3
Table 4 Selected V V distances (Å) for comparison between (I) and (III). Compound V V inter-layer V V edge-shared V V corner-shared (I) 5.650 (8) 3.330 (2) 3.704 (5) (III) 5.070 (6) 3.131 (4) 3.871 (3) Acknowledgements We thank EPSRC for a DTA studentship (EP/P505097/1) to CB. References Aidoudi, F. H., Aldous, D. W., Goff, R. J., Slawin, A. M. Z., Attfield, P., Morris, R. E. & Lightfoot, P. (2011a). Nat. Chem. 3, 801 806. Aidoudi, F. H., Byrne, P. J., Pheobe, A. K., Teat, S. J., Lightfoot, P. & Morris, R. E. (2011b). Dalton Trans. 40, 4324 4331. Aidoudi, F. H., Black, C., Arachchige, K. S. A., Slawin, A. M. Z., Morris, R. E. & Lightfoot, P. (2014). Dalton Trans. 43, 568 575. Aldous, D. A., Stephens, N. F. & Lightfoot, P. (2007). Dalton Trans. 2271 2282. Brese, N. E. & O Keeffe, M. (1991). Acta Cryst. B47, 192 197. Brown, I. D. & Altermatt, D. (1985). Acta Cryst. B41, 244 247. Clark, L., Aidoudi, F. H., Black, C., Arachchige, K. S. A., Slawin, A. M. Z., Morris, R. E. & Lightfoot, P. (2015). Angew. Chem. Int. Ed. 54. in press. Dai, Z., Shi, Z., Li, G., Zhang, D., Fu, W., Jin, H., Xu, W. & Feng, S. (2003). Inorg. Chem. 42, 7396 7402. Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565. Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837 838. Flack, H. D. & Bernardinelli, G. (1999). Acta Cryst. A55, 908 915. Flack, H. D. & Bernardinelli, G. (2000). J. Appl. Cryst. 33, 1143 1148. Kim, S.-H., Yeon, J., Sefat, A. S., Mandrus, D. G. & Halasyamani, P. S. (2010). Chem. Mater. 22, 6665 6672. Massa, W., Yakubovich, O. V. & Dimitrova, O. V. (2002). Solid State Sci. 4, 495 501. Nguyen, P. T., Hoffman, R. D. & Sleight, A. W. (1995). Mater. Res. Bull. 30, 1055 1063. Sheldrick, G. M. (2008). Acta Cryst. A64, 112 122. Spek, A. L. (2003). J. Appl. Cryst. 36, 7 13. Supel, J., Abram, U., Hagenbach, A. & Seppelt, K. (2007). Inorg. Chem. 46, 5591 5595. Figure 1 Fig. 1. Crystal packing of (I) viewed along the [010] direction. Figure 2 Fig. 2. The building unit of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at 50% probability. i = 1/2 x, 1/2 y, 1 z, ii = 1/2 x, 1/2 + y, 3/2 z 4
Figure 3 Fig. 3a. The layer of (I) along [100]. Fig. 3 b. The layer of (III) along [100]. By comparison with Fig. 3a. the same corner and edge-sharing configuration can be seen, with a terminal cis-water and fluoride ligand in (I) and (III) respectively. Figure 4 Fig. 4a. Polyhedral representation of (I), viewed along [010], perpendicular to the layers. Fig. 4 b. Polyhedral representation of (III), viewed along [010]. Note the differences in layer stacking, mediated by the presence of inter-layer water molecules in (I). 5
supplementary materials supplementary materials V 2 O 2 F 4 (H 2 O) 2 H 2 O: a new V 4+ layer structure related to VOF 3 Computing details Data collection: CrystalClear (Rigaku Corp., 2004); cell refinement: CrystalClear (Rigaku Corp., 2004); data reduction: CrystalClear (Rigaku Corp., 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Diamond (Brandenburg, 2009); software used to prepare material for publication: WinGX (Farrugia, 1999). (I) Crystal data F 4 H 6 O 5 V 2 M r = 263.93 Monoclinic, C2/c Hall symbol: -C2yc a = 14.453 (8) Å b = 4.8879 (19) Å c = 9.663 (5) Å β = 103.24 (2) V = 664.5 (6) Å 3 Z = 4 Data collection Rigaku SCXmini diffractometer Radiation source: fine-focus sealed tube Graphite monochromator dtprofit.ref scans Absorption correction: multi-scan REQAB (Rigaku, 1998) T min = 0.742, T max = 1.000 3138 measured reflections Refinement Refinement on F 2 Least-squares matrix: full R[F 2 > 2σ(F 2 )] = 0.035 wr(f 2 ) = 0.071 S = 1.01 750 reflections 63 parameters 0 restraints Primary atom site location: structure-invariant direct methods F(000) = 512 D x = 2.638 Mg m 3 Mo Kα radiation, λ = 0.71073 Å Cell parameters from 1673 reflections θ = 3.5 28.9 µ = 2.87 mm 1 T = 173 K Block, blue 0.06 0.04 0.03 mm 750 independent reflections 585 reflections with I > 2σ(I) R int = 0.115 θ max = 27.3, θ min = 2.9 h = 18 18 k = 6 6 l = 12 12 1080 standard reflections every 1 reflections Secondary atom site location: difference Fourier map Hydrogen site location: inferred from neighbouring sites All H-atom parameters refined w = 1/[σ 2 (F o 2 ) + (0.0095P) 2 ] where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.030 Δρ max = 0.56 e Å 3 Δρ min = 0.67 e Å 3 sup-1
supplementary materials Special details Refinement Refinement of F 2 against ALL reflections. The weighted R-factor wr and goodness of fit S are based on F 2, conventional R-factors R are based on F, with F set to zero for negative F 2. The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 ) x y z U iso */U eq V1 0.18501 (4) 0.19656 (10) 0.61917 (6) 0.00822 (18) F1 0.19765 (13) 0.4512 (4) 0.4665 (2) 0.0113 (4) F2 0.21071 (14) 0.1169 (4) 0.7467 (2) 0.0125 (4) O1 0.10702 (19) 0.0680 (5) 0.4776 (3) 0.0133 (6) O2 0.09784 (17) 0.3392 (4) 0.6657 (3) 0.0136 (5) O3 0.0000 0.1972 (8) 0.2500 0.0137 (8) H1 0.127 (3) 0.201 (9) 0.467 (5) 0.027 (14)* H2 0.070 (3) 0.001 (10) 0.403 (5) 0.036 (14)* H3 0.033 (3) 0.292 (8) 0.230 (6) 0.037 (16)* Atomic displacement parameters (Å 2 ) U 11 U 22 U 33 U 12 U 13 U 23 V1 0.0096 (3) 0.0066 (3) 0.0085 (3) 0.0004 (2) 0.0022 (2) 0.0001 (2) F1 0.0159 (11) 0.0086 (9) 0.0100 (10) 0.0018 (7) 0.0042 (9) 0.0012 (8) F2 0.0149 (10) 0.0092 (9) 0.0119 (12) 0.0009 (7) 0.0004 (9) 0.0039 (8) O1 0.0166 (14) 0.0084 (13) 0.0132 (15) 0.0010 (11) 0.0001 (11) 0.0019 (12) O2 0.0137 (11) 0.0114 (12) 0.0157 (15) 0.0022 (9) 0.0035 (11) 0.0009 (10) O3 0.0150 (18) 0.0108 (17) 0.015 (2) 0.000 0.0032 (16) 0.000 Geometric parameters (Å, º) V1 O2 1.592 (2) V1 O1 2.027 (3) V1 F2 1.948 (2) V1 F1 ii 2.174 (2) V1 F1 1.971 (2) F1 V1 ii 2.174 (2) V1 F2 i 1.972 (2) F2 V1 iii 1.972 (2) O2 V1 F2 102.39 (11) F2 i V1 O1 164.14 (10) O2 V1 F1 98.60 (11) O2 V1 F1 ii 171.78 (11) F2 V1 F1 159.00 (9) F2 V1 F1 ii 85.83 (8) O2 V1 F2 i 98.46 (11) F1 V1 F1 ii 73.18 (8) F2 V1 F2 i 86.65 (5) F2 i V1 F1 ii 81.86 (9) F1 V1 F2 i 90.68 (9) O1 V1 F1 ii 83.84 (10) O2 V1 O1 96.67 (13) V1 F1 V1 ii 106.82 (8) F2 V1 O1 85.48 (11) V1 F2 V1 iii 141.81 (11) F1 V1 O1 91.75 (11) Symmetry codes: (i) x+1/2, y+1/2, z+3/2; (ii) x+1/2, y+1/2, z+1; (iii) x+1/2, y 1/2, z+3/2. sup-2